In a dual fuel engine, a fuel injector is used to inject liquid fuel, such as diesel distillate, into the engine cylinder, and a second system is responsible for delivering a second type of fuel, such as natural gas. For such dual fuel engines it is desirable to be able to inject two distinct quantities of liquid fuel. A small pilot injection of diesel fuel is used to assist in ignition of a main charge of gaseous fuel when the engine is operating in dual fuel mode. However, when gaseous fuel is unavailable, or for some other reason diesel-only operation of the engine is desired, a larger injection of only diesel is made.
For a dual fuel injector that is configured to run both natural gas and diesel fuel (as a pilot), there are times when it would be desired to be able to operate with diesel fuel only. In an injector designed for 5% diesel fuel and 95% natural gas with two distinct orifice sets, the orifice size and number for the diesel circuit are undersized and there is a challenge for delivering diesel fuel during a diesel-only operation.
In the past, it would have been necessary to use two separate fuel injectors, or at least two separate nozzle assemblies in an engine in order to achieve these operating requirements. For example, one nozzle would have been necessary for the small initial pilot injection, and a second nozzle would have been necessary for the larger diesel-only injection. However, such systems tend to be complex and difficult to control. It is thus desirable to create a system capable of fulfilling the dual fuel injection requirements in situations when there is a deficiency in natural gas supply that causes the dual fuel engine to utilize a diesel-only operation until there is resumption in supply of natural gas to the engine.
U.S. Pat. No. 6,601,566 (the '566 patent) issued to Gillis et al. discloses a method of injecting fuel that includes a step of providing a fuel injector with a plurality of nozzle outlets and a directly controlled dual concentric check assembly. The injector has dual-check nozzles with separate orifices for pilot and main injection that are operated by electronic actuator control. The outer check has a relatively low valve opening pressure and controls a set of orifices with a smaller flow area. The inner check has a relatively high valve opening pressure and controls a set of spray orifices with a relatively large flow area. Combined with a standard unit pump or high pressure fuel common rail, the dual concentric check design provides a fuel injection system capable of higher initial injection pressures. However, the '566 patent fails to disclose the operation of the dual fuel engine when it would desired to operate with diesel fuel only.
It is therefore desirable to provide, among other things, an improved system and method for operating a dual fuel engine in limp home mode.